The present invention relates to a device for the automatic selection of one of a plurality of fluids forming the mobile phase in a chromatographic analysis apparatus.
It is known that at present the so-called high pressure liquid chromatography (HPLC) is a widely used analytical technique in analysis laboratories.
The instrumentation employed in the HPLC technique, schematically shown in FIG. 2, is represented by a chromatographic column 2 which operates under particular conditions of pressure, ensured by a suitable pump 11 for the passage of the mobile phase 10 (an appropriately selected mixture of solvents).
Generally the column is inserted in a thermostatically controlled system. The sample under examination (a solution thereof) is "injected", possibly by an automatic sampler 16, in the column wherein, through the action of the mobile phase, the various components are separated from one another and from possible impurities. The material eluted from the column is measured by a detector 13, the response of the latter being recorded in the form of peaks. The calculations necessary for determining the individual components are based on the areas or height of these peaks.
The recorder 14 may be replaced by an integrator/computer 15, which directly provides the analytical results.
The evolution of the technique has led to the marketing of instruments which make it possible to operate under automatic conditions. In the most recent arrangements, in fact, the HPLC chromatograph is equipped with an automatic sampler, i.e. with a device capable of performing the operations of injecting, in succession, a series of samples prepared beforehand. As, however, each type of product and thence each type of analysis requires clearly defined and specific instrumental conditions, it follows that the possibility of automation is limited to a series of homogeneous samples.
In practice, however, one is generally faced with the task of having to analyze several series of different samples, each of which requires different operating parameters and, in particular, different mobile phases.
With the most sophisticated devices it is possible to program certain variations of the machine's parameters and, as far as the mobile phase is concerned, it is also possible, starting with (up to 4) different solvents, to obtain mixtures with varying concentration of the solvents themselves, which enables an extension of the automation possibilities, but not to those cases requiring analysis of a large number of different series with, consequently, a large number of qualitatively different mobile phases. Complete automation can therefore be guaranteed even in the most unfavourable conditions, only when it is possible to change a large number of mobile phase automatically.
From U.S. Pat. No. 4,364,263 it is known a chromatographic system of the HPLC type wherein the solvents selector comprises a six-position rotary pneumatic valve for the inlet of six different mobile phases. Each control pulse supplied by the system CPU is converted to a pneumatic impulse capable of operating the valve.
This device has different inconveniences and limitations.
The number of mobile phases which are selectable is limited and depends upon the number of inlets of the valve. Therefore the possible increase of the number of possible phases would require the construction of an appropriate valve. Furthermore the pneumatic operation makes it indispensable an additional supply of compressed gas which brings about increased costs, encumberances and complexities. Lastly, changing from a phase to another implies a flow interruption, to allow the new positioning of the valve, as well as possible inconveniences deriving from moving mechanical parts.